On Wed, May 27, 2026 at 06:18:44PM +0200, Peter Zijlstra wrote: > On Tue, May 26, 2026 at 08:21:36AM -0700, Boqun Feng wrote: > > Hi Peter, > > > > This is a follow-up for Lyude's work [1]. After learning the current > > preempt_count() usage and how ARM64 handle this, I came up with this > > series that could resolve your feedback [2]. The basic idea is based on: > > > > 1) preempt_count() previously already masks our NEED_RESCHED bit, so the > > effective bits is 31bits > > 2) with a 64bit preempt count implementation (as in your PREEMPT_LONG > > proposal), the effective bits that record "whether we CAN preempt or > > not" still fit in 32bit (i.e. an int) > > > > as a result, I don't think we need to change the existing > > preempt_count() API, but rather keep "32bit vs 64bit" as an > > implementation detail. This saves us the need to change the printk code > > for preempt_count(). > > > > > v1: > > https://lore.kernel.org/rust-for-linux/[email protected]/ > > > > Changes since v1: > > > > * Rename PREEMPT_COUNT_64BIT to HAS_SEPARATE_PREEMPT_RESCHED_BITS per > > Mark Rutland. > > Blergh, so I really don't like that new name. It isn't that > PREEMPT_RESCHED is separate, it really is a 64bit preempt count. > > Shashiko has a few fits, but its mostly being stupid. Although I think > it might be useful to perhaps put a WARN_ON_ONCE(in_nmi()) in > local_interrupt_disable().
Yes, that's also what I'm thinking of, and also we need to check local_softirq_pending() in local_interrupt_enable() I think, because now HARDIRQ_DISABLE bits being non-zero means deferring softirq. (Shashiko also reported this as well). > > Anyway, I'll re-read things again tomorrow, but I suppose this will do. > Thank you! Regards, Boqun
